This invention relates to ground fault interrupters of the differential current transformer type.
It has been recognized that the trip circuit electronics of ground fault interrupters needs to be protected against transient voltage surges that may appear on the line. In the case of two pole apparatus, such surges may occur on either one of the line conductors between it and ground or neutral or between the two line conductors. It has been known in the past in both single and multipole apparatus to employ the solenoid trip coil in the conductor from the line to the trip electronics and utilize its substantial impedance to help suppress transients. Since the trip electronics frequently requires an operating supply that is rectified, there have been used elements such as full wave rectifier bridges, each including four diodes, between the solenoid coil and trip electronics, or, in multipole systems, between each of the solenoid coils and the trip electronics.
In U.S. Pat. No. 3,852,642 by Engel et al there is disclosed a sensing amplifier and trip circuit utilizing a half wave rectified supply that may be provided in the case of a single pole system by a single diode rectifier. It was with the purposes of providing a two pole ground fault circuit interrupter utilizing the referred to type of trip circuit and providing good transient protection as well as simplicity and economy of components that the present invention came about.